A multilayer type electronic part is manufactured by using either a wet stacking method or a dry stacking method. In the wet stacking method, the multilayer type electronic part is formed by repeatedly coating a ceramic paste and a conductive paste using a screen printing so as to obtain alternating ceramic layers and internal electrode patterns. In the dry stacking method, the multilayer type electronic part is formed by first forming ceramic green sheets, printing the internal electrode patterns on the ceramic green sheets using the conductive paste and screen printing, and then laminating the ceramic green sheets.
In the multilayer type ceramic inductor or the multilayer type composite part incorporating therein an inductor manufactured using the wet stacking method, the internal electrode patterns formed on the ceramic layers are subsequently electrically connected to each other to form a coil thereinside by coating the ceramic paste on each of the internal electrode patterns except for ends thereof and then coating the conductive paste on the ends.
In the multilayer type ceramic inductor or the multilayer type composite part incorporating therein an inductor manufactured using the dry stacking method, the internal electrode patterns formed on the ceramic green sheets are subsequently electrically connected to each other to form a coil thereinside by filling through-holes on the ceramic green sheets with a conductive material.
The laminated structure formed using either of the methods described above is diced and then is sintered. There is applied on the diced sintered laminated structure a conductive paste on two opposing sides thereof. The diced sintered laminated structure is then heated to allow the conductive paste to stick thereonto, forming external electrodes, resulting in the multilayer type electronic part.
The multilayer type electronic part manufactured in the manners described above, for example, a multilayer type ceramic inductor, is formed with the internal electrode patterns, the internal electrode patterns being stacked on top of another a direction identical to the direction in which the sheets constituting the laminated structure are stacked, resulting in the internal electrode patterns forming the coil. Both ends of the coiled internal electrode patterns function as the lead electrodes by being exposed at the above-mentioned opposing sides of the laminated structure, allowing them to be electrically connected to the external electrodes.
There is shown in FIG. 14 an exploded perspective view of the way in which the ceramic layers in the multilayer type ceramic inductor including a laminated structure 11 are stacked using the dry stacking method. As shown, the laminated structure 11 includes a plurality of stacked ceramic layers 1, 1 . . . , 1', 1' . . . .
The ceramic layers 1, 1 . . . , made of a magnetic material, are respectively formed with internal electrode patterns 5a-5d. The internal electrode patterns 5a-5d are subsequently electrically connected to each other by filling through-holes 6, 6 . . . with a conductive material in such a way that they form a coil inside the laminated structure 11 by being stacked on top of each other in a direction identical to the direction in which the layers are stacked in the laminated structure 11. The ceramic layers 1, 1 . . . act as a magnetic core of the coil.
As shown in FIG. 14, the ceramic layers 1, 1 which are, respectively, located at bottom and at top of the laminated structure 11 are, respectively, formed with the internal electrode patterns 5c, 5d, wherein one of the ends of each of the internal electrode patterns 5c, 5d functions as the lead electrodes by being located opposing side from each other in the laminated structure 11 and being exposed.
Above the top ceramic layer 1 and below the bottom ceramic layer 1 are, respectively, disposed the ceramic layers 1', 1' . . . which are not formed with the internal electrode pattern. These ceramic layers are known as blank ceramic layers.
The laminated structure 11 further includes a pair of external electrodes (not shown) at the opposing sides thereof, the external electrodes being formed by applying a conductive paste, e.g., silver paste, on the foregoing opposing sides and heating the laminated structure 11 to force the conductive paste to stick thereon. In this case, if desired, a nickel coating or a solder coating may be additionally applied thereon. The external electrodes are electrically connected to the lead electrodes 4, 4.
In addition, the multilayer type composite electronic part may include, for example, a multilayer type LC part incorporating therein an inductance portion as well as a capacitor portion.
In such multilayer type electronic parts, the inductance can be varied by changing the number of turns in the coil or by changing the permeability of the magnetic material. However, in changing the inductance using the former method, since the external dimensions of the multilayer type electronic parts are usually fixed, the number of turns in the coil can be changed either by increasing the thickness of the ceramic layers or by reducing the number of the ceramic layers 1, 1 . . . having the internal electrode patterns 5a-5d and increasing the ceramic layers without the internal electrode pattern printed thereon.
In order to increase the production efficiency in manufacturing the multilayer type electronic parts, it is desirable to standardize the ceramic green sheets for forming the laminated structure and use the standardized ceramic green sheets to manufacture the multilayer type electronic parts having different inductance values from each other. Currently, however, the ceramic layers having different permeability from each other or the ceramic layers having different thickness from each other are used in manufacturing the multilayer type electronic parts different from each other in their performance characteristics, necessitating various types of ceramic green sheets to be prepared in advance, which, in turn, will reduce the production efficiency.
On the other hand, in using the ceramic green sheets used in manufacturing the multilayer type electronic parts with high inductance in manufacturing the multilayer type electronic parts having low inductance, the number of ceramic layers having the internal electrode patterns must be reduced and the ceramic layers without the internal electrode pattern must be increased accordingly.
However, when the multilayer type electronic parts are manufactured using the thin ceramic layers in order to obtain a relatively small inductance value, the multilayer type electronic parts become saddled with an unwanted stray capacity due to capacitance generated between the internal electrode patterns of the ceramic layers. To be more specific, in the multilayer type ceramic inductor, when the number of turns in the coil is reduced to obtain a relatively low inductance, the stray capacity thereof increases, resulting in deteriorating the performance characteristics of the multilayer type ceramic inductor.